With the dramatic development of semiconductor technology in recent years, complementary metal-oxide-semiconductor (CMOS) bio-sensors have been integrated with CMOS circuit, which make the realization of CMOS biomedical system on chip (SOC) possible, leading to miniature and low cost biomedical systems.
In general, biomedical or physiological signals have characteristics of ultra low-level signals with wide dynamic range. U.S. Pat. No. 5,206,602 published on Apr. 27, 1993, titled “Biomedical amplifier circuit” disclosed an electronic differential amplifier circuit comprising: a first stage amplifier means, a second stage amplifier means, second stage common mode feedback means, and gain feedback means is a mixed analog and digital integrated circuit (ADC) with features which are especially useful for application as a front end for physiological signal instrumentation such as electrocardiography (EGC), electroencephalography (EEG), electrogastrography (EGG), electromyography (EMG), electroneurography (ENG), electro-iconography (EOG), electroetinography (ERG).
Furthermore, with reference to FIG. 1, an CMOS circuit is a conventional programmable-gain amplifier (PGA) 1, and the PGA (1) comprises an instrumentation amplifier (IA) (11), an amplifier (12) coupled to the back of IA (11), a multiplexer (13) and a digital control interface (14), wherein the amplifier (12) is controlled manually through the multiplexer (13) and the digital interface (14), to amplify the biomedical signal be proceeded within a range of back end circuit. It is necessary for the PGA (1) to seize more space to encompass such as the multiplexer (13), the digital control interface (14) and etc; therefore the architecture of the PGA (1) has a defect of chip area requirement. Consequently, the PGA (1) can neither conform to the trend of miniaturization nor make realization of biomedical system on chip (SOC). Moreover, the gain of the PGA (1) is required to control by people externally.
The above-mentioned circuits are belonged to a type of feedback circuits, utilize to proceed the biomedical signal, nevertheless, generating the noise signal and caused the bigger measurement error value when the circuits output the signal, consequently, the signal is not effective to be applied in bio field, which required precise signal for user to interpret.